2014 Post-winter Topeka Shiner Survey

After one of the coldest and driest winters on record in North-central Iowa, biologists from the Rock Island Field Office seined restored oxbow ponds to determine overwinter survivability of Topeka shiners. During harsh, long winters fish kills can easily occur in lakes and ponds. When snow and ice cover the surface of a pond for a prolonged period of time sunlight is unable to reach the pond’s bottom, and plants begin to die. As the dead plants decay the oxygen in the pond is consumed by the bacteria decomposing the dead plants. Most fish cannot survive once dissolved oxygen levels get below a certain point. The prairie pothole region in Iowa had already suffered through two of the driest years on record in 2012 and 2013. Ponds and lakes in that area were already extremely low heading into the winter. This combined with the fact that it was so cold for so long made for very tough living conditions for fish. Fish kills were being reported all over the area, so biologists feared that restored oxbow ponds that were known to contain Topeka shiners last fall had also been affected.

On April 16th biologists checked four restored oxbows that were all known to contain Topeka shiners. All of the oxbows checked did indeed have a fish kill of some degree. The edges of all of the oxbows were littered with dead fish of all different sizes. The majority of the dead fish were carp and green sunfish. Biologists used a bag seine to very effectively sample the entire oxbow to check for any survivors. Two out of four oxbows sampled did have complete winter kills to the point where even tadpoles and crayfish were dead. A third oxbow sampled was found to contain only a handful of black bullheads and fathead minnows. The fourth oxbow sampled that day contained only two fathead minnows and four juvenile Topeka shiners! When that oxbow was sampled in July 2013 it was found to contain 1,790 fish of 16 different species, including 10 adult Topeka shiners. The fact that Topeka shiners were able to survive such harsh conditions when almost all other fish and aquatic animals perished is a true testament to how hardy these fish are. It also demonstrates that this little native prairie fish was built to survive in these types of habitats when other species like the introduced carp were not.

Although all of the oxbow ponds had some degree of winter, some live Topeka shiners were found. USFWS biologist Aleshia Kenney shows one of these small native fish.

Photo by USFWS; Kristen Lundh

Off-channel habitats have been known to be an important part of the Topeka shiner’s lifecycle in Iowa. The fact that Topeka shiners were able to overwinter in a restored oxbow when the nearby stream was almost completely dry and frozen solid reinforces how important these habitats truly are for this endangered fish. Last year’s adult Topeka shiners that survived the drought in that oxbow were able survive and reproduce. A few of their progeny were then able to survive one of the coldest winters on record when almost all of the other fish around them perished. Hopefully this cycle will continue until a flood occurs and allows for immigration/emigration into and out of the oxbow. Strategically placing sustainable off-channel habitats along Critical Habitat streams may be a key step towards recovery of this endangered species, especially as the climate continues to change.

Climate models predict that extreme weather events will become more frequent. Extreme weather years are the years that biologists need to design these restorations for. We know that during normal years these restored oxbows will support fish year round. What we need to figure out is why two of the oxbows we sampled were able to support fish during such an extreme event when others around them were not. These differences could be the key design features to achieving overwintering success in all of our restored oxbows, and move us one step closer towards recovery of the Topeka shiner.